1. Field of the Invention
The present invention relates to a liquid crystal display device and method for fabricating the same.
2. Description of the Prior Art
Generally, liquid crystal is a material having a behavior intermediate between liquid and solid, namely, having both a fluidity of liquid and an optical property of crystal. When such a liquid crystal is subjected to an electric field or heat, its optical anisotropy may be varied. Liquid crystal display devices aye adapted to utilize such a behavior. Such liquid crystal display devices ale representative of planar display devices, together with plasma display devices and light emitting devices.
Liquid crystal was discovered in the year 1888 by Reinitzer who was a Australian botanist. Subsequently, there were made various physical and chemical researches in liquid crystal, In the year 1963, Fergason developed a thermography using cholesteric liquid crystal. By virtue of this development, researches in liquid crystal become active again.
In particular, Heilmeier in RCA corporation who was realized of the limitations of performance of EL panel discovered the phenomenon that a transparent thin layer of nematic liquid crystal becomes white-cloudy by an electric field, during his seeking for display devices as a substitute for the EL panel in the year 1968.
FIG. 1 is a plan view illustrating a conventional liquid crystal display devices. FIG. 2 is a cross-sectional view taken along the line I--I of FIG. 1.
AS shown in FIGS. 1 and 2, the conventional liquid crystal display device includes a lower glass plate 9, an upper glass plate 10 vertically spaced apart from the lower glass plate 9, a pair of oxide films 11 adapted to prevent attachment of alkali ions to the glass plates 9 and 10, a pair of transparent electrode films 12 comprised of an indium tin oxide (ITO) layer having a certain pattern and applied within voltage, a pair of top coating films 13 adapted to prevent a short circuit of the transparent electrode films 12, and a pair of facing orientation films 14 defining a space containing a liquid crystal 15 therebetween.
In the space defined between the orientation films 14 respectively attached to the glass plates 9 and 10, a plurality of spacers 17 are arranged. The liquid crystal fills the remaining part of the space. The glass plates 9 and 10 are sealed with a seal 16. Polarization plates 18 are attached to outer surfaces of the glass plates 9 and 10, respectively.
The transparent electrode films 12 respectively formed on the glass plates 9 and 10 are arranged orthogonally with respect to each other. The glass plates 9 and 10 are sealed with the seal 16 along a seal line. The region A of FIG, 1 is a display region where the transparent electrode films 12 of the glass plates 9 and 10 are overlapped with each other. At the region B other than the display region A and defined inwardly of the seal 16, only one of the transparent electrode films 12 is disposed.
In a case of a super twist nematic (STN) liquid crystal display device requiring a more accurate cell gap, such a structure results in a color difference in the liquid crystal display, because there is a difference in total layer thickness by the thickness of one transparent electrode film.
In other words, the transparent electrode films 12 of the STN liquid crystal display device requires several ohms per meter and is comprised of an ITO film having the thickness of several hundred angstroms to several thousand angstroms. The liquid crystal display device has a portion involving a thickness difference by the thickness of one transparent electrode film 12 between the display region A where the transparent electrode films 12 are overlapped with each other to vary the twist of liquid crystal and the region B other than the display region A.
As a result, it is difficult to obtain an accurate cell gap due to the thickness difference corresponding to the thickness of one transparent electrode film 12. Due to such a cell gap difference caused by the thickness difference between the display area and the area other than the display area, the liquid crystal display device involves a difference in color display and thereby a degradation in display quality.